Landfill gas, which is recovered from decomposing refuse in landfills, typically contains methane and carbon dioxide as major constituents and various impurities, such as water, nitrogen, hydrogen, chlorinated hydrocarbons and other organic compounds. By removing some, or most, of the impurities, landfill gas containing a higher percentage of methane is produced. The impurities can be removed in various different ways, including the manner disclosed in Bingham U.S. Pat. No. 4,000,990.
The chlorinated hydrocarbons are typically present in relatively small amounts in landfill gas. However, if these components are present in more than negligible concentrations, corrosive acid may form under conditions of compression and combustion. Accordingly, it is important to obtain an accurate analysis of the raw landfill gas and partly purified landfill gas so that the concentration of the chlorinated hydrocarbons in, for example, parts per million, can be accurately determined.
Unfortunately, the only equipment for accomplishing this in the prior art is a gas chromatograph-mass spectrometer. This equipment is very expensive and does not provide sufficiently accurate information as to the concentration of the chlorinated hydrocarbons.
Gas analysis for certain gases can be performed with a gas chromatograph. A conventional gas chromatograph includes a gas chromatograph column containing a column packing capable of separating the gas components and a detector for detecting the concentration of the gas components separated by the column. The gas to be analyzed is carried through the column by a suitable carrier gas. The column packing of the column may be, for example, an adsorbent which adsorbs the components of interest and separates them so that each gas component of interest is sequentially provided at the output of the column. Temperature programming of the column can be used to decrease elution time.
There is no commercially available gas chromatograph system of which we are aware that will provide the concentration of the particular chlorinated hydrocarbons found in landfill gas. More specifically, column packings that will separate the unusual list of chlorinated hydrocarbons commonly found in landfill gas are not known. Also, the particular temperature control necessary to bring about the relatively rapid separation of the chlorinated hydrocarbons is also not known.
In using of a gas chromatographic system, a sample gas can be loaded into a receiver. To inject the sample gas into the chromatographic column, a carrier gas is loaded into the receiver and allowed to carry the sample gas to the column. With landfill gas, we have found that it is sometimes desirable to use a marker gas having a composition not found in the sample and which will be separated by the chromatographic column from any of the sample components. Thus, the marker gas represents a starting point or benchmark for the detection process. The conventional gas chromatographic system provides no suitable way for injection of the marker and of the sample gas, nor does it provide a convenient manner for making redundant tests of the sample gas.